FIG. 1 is a diagrammatic showing of the configuration of a conventional communication network system, in which base stations 1 and 2 of radio zones respectively E1 and E2 are interconnected through a public switched telephone network 3. Radio terminals A to F in radio zone E1 communicate with the base station 1, for example, by frequency division multiple access (FDMA) or time division multiple access (TDMA).
In this instance, when radio terminals A to F are used as ordinary telephones, the amount of data for communication (hereafter communication data) is constant, and hence they need only to be assigned a radio channel of a fixed channel capacity. However during data communication, the amount of communication data increases or decreases according to the state of access. When the amount of communication data increases, if such channel capacity factors as the number of channels and slots and the frequency bandwidth remain unchanged despite an increased amount of data, resources run short which results in a failure to achieve a satisfactory transmission speed. On the contrary, when the amount of communication data decreases, the degree of unused resources increases and radio channels are not effectively used.
To overcome the above drawbacks, a method has been proposed which employs small-capacity and large-capacity radio channels each provided separately and selectively switches them according to the amount of communication data as disclosed, for example, in Pat. Appln. Laid-Open Gazette No. 97824/96.
However, when the number of communication terminals that use only the small-capacity radio channels is larger than the total number of small-capacity radio channels, some of the communication terminals cannot be assigned radio channels. Furthermore the assignment of large-capacity radio channels to such communication terminals will inevitably give arise to a problem of ineffective use of radio channels.
The present invention is intended to solve the above problem, and has the object of increasing the speed of data communication and reducing waste in the use of radio channels through the effective utilization of a limited number of channels on the basis of changing the number of channels, the number of slots, the frequency bandwidth, or similar channel factors in accordance with the amount of communication data or the rate of change in the amount of communication data per unit time.